In order to prevent an occupant from bumping against a side member in a compartment of a vehicle, for example a door, in a lateral collision, an air bag device may be mounted to the door. When the vehicle suffers a lateral collision, the air bag device against lateral collision starts to deploy an air bag. To detect a lateral collision, sensors mounted to the vehicle sense acceleration in the lateral direction of the vehicle. When the acceleration exceeds a predetermined value, a decision circuit determines that a lateral collision occurs to the vehicle and then supplies a starting current to a gas generator of the air bag device.
In a conventional air bag device against lateral collision, an air bag is covered by a module cover which is broken at the deployment of the air bag so that the air bag is extended toward a compartment of the vehicle.
In the conventional air bag device against lateral collision, since it is necessary to apply pressure for breaking the module cover to the module cover, a gas generator having large capacity must be employed.